Shock absorber



Jan. 2. 1945. 5 FOCHT 2,366,248

SHOCK ABSORBER Filed Feb. 24, 1943 2 Sheefs-Sheet 1 Jan. 2. 1945. N. 3. FOCHT snocx ABSORBER 2 Sheets-Sheet 2 Filed Feb. 24, 1945 sired point spaced above the point of pivotal connection of the arm |6 therewith. The shock absorber thus serves as a telescopic strut between the strut I4 and the arm 16 and by its telescopic action in response to upward and. downward swinging movement of the arm I6 as the weight of the airplane is imposed upon and removed.

from the landing wheel I1, acts to cushion or absorb the forces which produce said movements of the arm l6.

Alternatively, the shock absorber may be conplane and at its lower end may carry a landing wheel, or it may be installed for dilerent uses in varous different ways without changin its general mode of operation.

Referring now in detail te the mechanism of the shock absorber, it will be observed that the head |2 of the cylinder I has fixed thereto and extending upwardly therefrom, centrally there0f, a smaller c'ylinder 20 which is closed at its upper end by a head 21, and. that-fixed to and extending downwardly from the head l3 of the piston Il, centrally thereof, is a piston rod 22 which extends through a. central opening in the head 2| into the cylinder 20 and within said cylinder 20 carries a piston head 23. In addition, it will be observed that the lower ends of the cylinders l0 and 20 are in communication with each other as, for example, through openings 20 in the cylinder 20.

It will further be observed that the lower end of the piston Il has fixed thereto a. ring-like piston head 24 which is disposed in thecylinder I0 in surrounding rlationship to the cylinder 20 and which is provided with suitable packings 25 and 26 to aiord liquid-tight seals between the same and said cylinders I 0 and 20.

In the piston head 24 is a loneitudinally extending bore 21 which is in communication with nected at its upper end to the fuselage of anairas indicated at l9, with the strut I4 at any delying the upper end of said tube to be engaged by the upper end of the metering pin stem 33 when the said upper end of said stem is projected above the top of said tube.

At a point suitably spaced from the bore 21 the cylinder head 24 has formed therethrough in side to side relationship to each other a, pair of:

small bores and 39 which alord communication between the cylinder I0 and the interior of the piston H under the control of a. pair of downwardlyelosing, upwardly opening check valves' 40 and 4l, respectively, which may be either of the ball type shown 01 of any other suitable type. In

any event, a. cam lever 42 extends from the piston head 24 upwardly into the hollow piston I 1 and. is

pivoted at its lower end, as indicated at 43, to said piston head 24 or inward and outwardswinging movement; a. tongue 44 extends outwardly from said lever into overlyng relationship to the valves 40 and 4l; coil springs 45 and 46 are interposed between said tongue and said valves, respectively; and react from said tongue to urge said valves lever 42 rides against the lip 47 and, according to the contour of its inner edge, said cam lever aslength or cooperation with the orifice 28 to vary the eective area thereof. Moreover, said metering pin includes a stem 33 extending upwardly from the valve portion 3l thereof into a guide tube 34 which may be either integral with 01 separate from the piston head 24. In adddition, a spring 35 tendsconstantly to urge the mtering pin 30 downwardly to its limit of downward movement in which its valve portion 3| closes the orifice 28, and suitable stop means is provided to limit upward movement of said pin against the force of the spring 35, said stop means being aiorded, for example, by the lower end of-the guide tube 34 which is engageable by the valve portion 3! of is anchored at one end to the top of the piston head 24 at a point rem0te from the tube 34, as indicated at 31, and has its-other orfree end over tended relative to each other.

of the inner edge of the cam lever 42s such that said lever is swung to its outermost position and thereby places the springs 45 and 46 under maxi mum compression when the cylinder 10 and the piston llare moved to their outermost or fully extended position relative to each other and that in response to inward movement of said cylinder I0and said piston II relative to each other-from their outermost position in which the cam lever 42 is in its outerinost position, said cam lever is permitted to swing gradually inward to progressive1y decrease the co'mpression of the sprngs 45 and 46.

The shock absrber is charged with enough liquid to fill the cylinders in and 20 and to cover the piston 24 and the head of the cylinder 20 when the cylinder |0and the piston l l are fully ex- I-Iowever, the amount of space within the piston |I above the level of the liquid therin when the shock absorber is fully extended is more than ample to accom modate al] of the liquid that is forced from the cylinders 10 and 20 by inward. movement of said cylinders and the pistons I I and 23, relative 'to each other to their limit of relative inwafd movement.

In the piston 23 is a valve mechanism of any suitable type through which liquid fiows from the lower end of the cylinder 20 into the upper end of said cylinder when said cylinder and said piston move inwardly relatively to each other, and which serves to regulate or meter return flow of liquid from the upper end to the lower end of said cylinder as said cylinder and thepiston 23 move outwardly relative to eachother under the influence of recoilforces imposed onthe shock cushionor absorb suchiorces. "Ihisvalve mechanism may be of the same constructon and mode of operation as the piston-carried -valve mechanismfor the Same generalpurpose illustrated,- -descriloed andclaimedin my prior applicaton,

Serial No. 4:63925,fi16d October 30, 1942, now

Patent No. 2,342,729 issud February 29, 1944,

and since no novelty in respect to the same, per se, is claimed herein, it is illustrated on1y by dotted 1ines and is designated generally as 48.

One of the springs 45, 46 is stronger than the other and both of said springs are at a11 tmes onder such compression and are of such strengths that, foreach diiferent stroke position of the shock absorber, the va1ves 40, 41 are maintained closecl against the calculated maximum liquid pressurein the cylnder Il) which the shock abuniformly throughout its stroke to cushon oi sorber, in operationunder normal conditions, is

designed to reliev by metered flow of liquid trom the cylinder ii|into the hollowpiston II through the orfice 28. On the other hand, the yieldable closing forces exerted upon the valves 463, 4! by the springs 45, 46 in each different stroke position of the shock absorber is such that if the pressureof the liquid exceeds the pressure which the shock absorber, in its operaton under norma1 conditions, is designed to re1eve byflow oi liquidthrough the orfice 28, one or both of said valvs s opened depending upon whether the abnormal pressure is oniy moderately or excessively Assuming that the shock absorber is installed in an airplane landing gear and is fullyextended and" that the airp1aneisiandng, the operation of the shock absorber is as ollows: upon the wheel Ilstriking the g'round and the weight of the airpiane thereby being imposed upon the shock absorber, thecylinders Ifl and and thepistons I;l and 23, respeqtively; are moved inwardly rela- -tiveto eachother at a velocity depending upon the. weight of the airplane and its decending ve locty, and as a result the liquid in the 1ower ends of the cylinders l and 20 -issuojected to pressure" and is forced from the said lower ends of said cylinders. Part of the liquid in the 1ower end. of the cylinder 20 flows through the valve mechanism 48 into the upper end of said. cylinder.

Due, h0wever, to the presence of the piston rod 22 in the upper end of the cylinder 211 the said upper end of sad cylinder cannot accommodate all of the 1iquidi that is forced from the lower end. thereof. Therefore, that portion of the 1iquid in the lower end of said. cylinder 20 Which cannot be accommodated in said cylinder above the piston head 23, is forced through the openings 2 into the cylinder H) On the other hand, all of the liquid that is forced from the lower end of the cylinder lflows into the hollow piston H either through the orfice 28, the bore 2'| andthe -opening 2.9, orthrough one or the otheror both of the checkwalve-controlled bores 38, 39, depending upon the vel0city of inward movement of the cylinder I0 and the piston H relative to each other and the consequent pressure to which the If thelanding is a normal one; i. e. anything less than a crash landing, the pressure and vel'octypf the liquid issuch as not to open either of the va1ves 49, M, but to act upon the -va1ve portion 31 of the -metering pin 30 to rase said va1ve porton off saidseatandthereby raise sad mctering pin, thus to cause the portion 32 of said metering pin tdcooperate With the orfice 28 to relate its efl'ectve area ami thereby regulate flow of the liquid 'from the cylinder II1 into the hollow pistonll.

The spring 35 is of such strength that the metering pin 30 is raised a definte amount byeach dierent pressure and velocity of the liqwid under normai or anything less than crash landing conditons, and the portion 32 of said metering pin is of such cross sectional areas at different points a1ong tslength that for each diierent position of theumetering pin, the effective area of the orfice 28 is such as to permit the exact amount of by-pass ofliquid through said orfice from the, cylinder Il3 into the hol1ow piston I I to afiord the required resistance by the shock absorber to the load imposed thereon. Thus, the shock absorber, under normal conditions, operates substantially absorb impact 1oads to which it is subjected.-

As liquid is forced nto thehollow piston II it compresses the air in said piston and this com pressed air acts as a resiient support for the weight of the airplane. Accordingly, when the airplane coines to rest, the liquid pressure in the cylnder H) is balanced against the air pressure in the piston H and the airplane therefcre has a soft, flexible taxiing condition. This is par- -ticularly true since, although the va1ve portion 3! of the meteringpn 3l closesthe orfice 28 under the influence of the spring 35 whenthe liquid and the air pressures in the shock absorber are balanced, the portion 32 of the metering pin of least cross sectional area is located at the upper end of said portion 32 to enter the orfice -22 si-- multaneously with upward movement of thevalve portion 3! of said metering pin off its seat. Consequently, a11 slight opening movements of the va1ve portion 3I, such as occur during norma1 taxiing of the air plane, result in the orfice 23 having amaximum efiective area for free fiowoi 1iquid therethrough in response to normal impact forces imposed upon the shock absorber as a re su1t of the aircraft encountering slight, obstructons -or elevations on or in theground or other surfaceover which it maybetaxiing, thus in but to permit a rapid by-pass of 1iquid from the cylinder II into the hollow piston Il) to case the initial landing impact of the airplane.

sive1y increase its resistance to the loadimposed thereon whereby it acts smoothly to ro ressive 1y absorb the 1oad.

In the event of an abnormal or crash landing, the high velocity and pressure of the liquici wi11 result in the metering pin 3!] being prpjected quicklytoitsi uppermost position as determined by engagement of its va1ve portion 3! With the stop constituted by the lower end of the tube 34,

and in turn this wll resu1t in the effective area of the orfice 28 being reduced to a minimum.

Since, then, the 1iquid cannot flow through the orfice 28 at a sufiiciently rapid rato properly t0 absorb the 1oad suddenly imposed upon the shock absorber, first the valve M1 or 4! that is held clcsedby theweaker spring- 45 or 4 6 opens and "Ihereafter, the efiective area of the orfice '28 decreases to cause the shock absorber to progresthn, ifnecessary, the other of saidvalires opens, under the high pressure of the liquid to permit flow of theiiquid through one or both of the bores 38, 39 into the hollow piston II to quickly relieve the excessively high pressure. Thereupon, the valve, or valves, 40, H, as the case rriay Hoe, is, or are, closed by the spring, or sprngs, 45, 46 andijthe metering pin 30 assumes a position, as determined by the reduced pressure and the velocityof theliquid, properly to control its flow through the orifice '28.

The 1eaf spring 36 acts to bui ra-pid upward projection of the metering pin 30 ioeyond the uppermost positiori which'said metering pin assumes in controlling norma1 impact 1oacis imposed upon the shock absorber, while, obviously, the cam lever 42, in conjunction with the stop or cam actuator 41, varies the strength of the springs 45, 46 in harmony with varying stroke positionsof the shock absorber so that for each different stroke position of the shock ahsorber one or the other or both of the valves 40, 4! will open only under a pressure of the liquid in excess of, but only slightly in excess of, the pressure which the shock absorber is desi-gned to relieve through the orifice 28. Thus, the shock ahsorber is high1y and substantially uniformly eflicient throughout its stroke in absorbing impact 1oads imposed thereon and yet is efifectively protected against harm by excessivly high pressures ger1erated therein and at the same time serves to protect the airplane against harm vinder severe impact 1oads.

The energy of recoil of the shock absorber is dissipated on the one hand b the va1ve 48 in the piston 23 acting to meter flow of 1iquid from the portion ofthe cylinder v20 above said piston 23 to the portion of said cylinder be1ow said piston, al] as more ful1y illustrated and as described in my aforesaid prior application, Serial No, 463,925, and also by flow of liquid from the hollow piston I I to the cylinder I through suitable passageways 49 in the piston head 24 under the control of a check valve 50 which opens toward the cylinder I0 and c1oses toward the hoilow piston 11 and which constantly is urged tofrom the spirit of the invention and scope of the appended claims.

I claim:

1. A shock absorber comprisingz, pair of members inovable relatve to each other by imposition upon the shock absorber of a force to be resisted, said shock absorber having a, liquid-containing chamber wherein the 1iquid is subjected to pressure by movement of said members relative to each other in response to imposition upon the shock ab'sorber of a force to be resisted and further having an rfice or outletof liquid from said chamber, means operable in response to the pressure and the velocity of the liquid to regu- 1ate its rate of flow through said orifice, yieldab1y closed pop-off valve means for the relief flow of liquid. from said chamber whenever the pressure of the liquid in said chamber exceeds a nredetermned va1ue, and cam and cam actuamembers relative;to each other .to vary the force tor means operablein response to shock absorberstroke movements of said members relative t0 each otherto impose a different predetermined yieldable closing orce upon said pop-0 va1ve means for each different stroke position of said members relative to each other.

2. A shock a:bsorber comprising a, pair of members movable relative to each other by imposi-. tion upon the shock absorber of a force to be resisted, said. shock absorber having a liquidcontaining chamber wheren the liquid is sub- .ected to pressure oy movement of said members relative to each other in response to imposition upon the shock absorber of a force to be resisted and iurther having an orifice for outlet of 1iquid from said chamber, means operable in response to the pressure and the velocit; of the liquid to regulate its rate of flow through said orifice, means including a pair of popoff valves for the re1ief flow of lquid from said chamber wheri.- ever the pressure of. the liquid. in said chamber exceeds a predetermined value, a separate yie1dab1e means for ciosing each of said valves, one of said yieldable means being stronger than the other so that only one of said valves opens under a. given excessive pressure of the liquid and the other opens under a higher excessive pressure of the liquid, and means operahle in response to shock absorber stroke movxnents of said members relative to each other to vary the pressures eXerted. by said yieldable means upon said valves in proportion to the strengths of said yeldable means.

3. A shock absorber cmprising a pair of memthe relief flow of liquid from said chamber whenever the pressure of the liquid in said chamioer exceeds a predetermined value, a spring maintaining said pop-0 va1ve normaliy closeda pivoted lever operable by swinging movement theraof te vary the pressure of said spring, and means operable in response to shock absorber stroke movements of said members relative to each other to swing said lever so that for each diierent stroke position of said members relativa to each other said spring exerts a different predetermined closing pressure upon said pop-off valve.

4. A shock absorber comprising a pair of members movable relative to eachother floy imposition upon the shock absorber of a orce to be resisted and further comprising a liquid-containing cham- =ber in which the 1quid is subjected to pressure by movement of said members relative t0 each other in r'esponse to imposition upon the shock absorber of a force to be resisted,- valve means to be opened by the pressure of the liquid to control flow of the 1i quid from said chamber. yieldable means exertng a closing force upon said. valve means, and cam and cam actuator means operativein response to movement of said of said yieldable meansexerted upon said vaiv means.

5. A shock absorber comprisin a pairof members movable relative to each other floyirnppsi-p tlon upon the shock absorbr of a force to be resisted and further comprising a liqud-contaning chamber in whch the liqud is subjected to pressure by movement of sad members relative to each other in response to imposton upon the shock absorber of a force to floe ressted, a

pair of valves to be opener]. by the pressur'e of theliquid to permit relief flow of the lquid from sa.id charhber, a separate yieldable meanstending constantly to c1ose each of said valves, sad valves beng of such areas and saidyieldable 1 means being of such stiengthg chat one of said valves opens under a gven pressure and the otherepens only under a higher pressure of the lqud, and means operatve inresponse to shock absorber stroke movements of said members relatve to each other to vary the pressures exerted by said yieldable meansupon said va1ves in proporton to the strengths of said yieldabl means.

6. A shock absorber comprsing a pair of members movable relatve tojeach other by impositon upon the shock absorber of a force to be resisted and urthr comiarsing a lqud-contanng chambern whch the lquid issubjected to pressure by movement of said members relatve to each other in response to mposton upon the shock absorber of a force te be ressted, a pair of vaves to be opened by the pressure of the 1iquid to permt re1ief flow of the1qud from sad chamber, a separate yeldablemeansjtendng' Constantly to close each of sacl vallves, sad va1ves being of such areas and sad yeldable means being of such strengths that one of said valves opens under a given pressure and the other opensonlyunder a higher pressure of the liqud, and cam and cam actuator means common to both of saidyelda-ble means and operatve in response to shock absorber stroke rnovements of sad members relative to each other to vary the pressures exerted by said yieldable means upon sad valves in proporton to the strengths of sad yie1 dable means, 

